Custom LESS should be validated prior to course build

[taylortom]

Expected Behaviour

It would be nice if we could validate the custom LESS prior to building a course, and therefore give the user a useful error.

I don't think it makes sense to try and catch this during the course build process later on, as it'd need some modification of the framework's grunt process.

Actual Behaviour

You're able to save the invalid LESS, and are then shown a generic error when you later try to build the course.

Steps to Reproduce

1. Add invalid LESS to Project settings > Custom LESS
2. Save
3. Attempt to preview

[tomgreenfield]

Validation of Less before compilation into CSS isn't really feasible; Ace certainly doesn't offer it.

May be more productive if we have better logging of errors into SweetAlert, e.g. doing something with:

Fatal error: {
 "type": "Parse",
 "filename": "src\\theme\\57079b40794fc3a4029e30f2\\less\\zzzzz.less",
 "index": 24,
 "line": 2,
 "callLine": null,
 "column": 15,
 "extract": [
  ".block {",
  "    @fake-mixin;",
  "}"
 ],
 "message": "directive options not recognised"
}

[taylortom]

Look into if we can lint/validate using backbone-forms

[lc-thomasberger]

Validating before build is a bit tricky, as most less errors will depend on the selected theme. For instance, certain variables or mixins are not defined in the selected theme.

For error handling on build, a feature to skip the custom less would be nice in case it breaks a build.